The invention relates to thermosetting reactive resin mixtures and moulded articles and coatings made therefrom.
Large numbers of thermosetting resin mixtures, which form cross-linked systems at raised temperatures, are known.
Paint binders, which contain carbamate groups--especially hydroxyalkyl carbamate derivatives--are likewise known and are relatively often used.
In such cases the function of the carbamate compounds used is quite varied.
Thus many binders for coatings, which contain low molecular weight hydroxyalkyl carbamates have been described. For example, such systems are the object of U.S. Pat. No. 4,520,167, EP 212 380, EP 302 222, WO 87/00851 and WO 88/02766. Similar thermosetting mixtures are described by W J Blank (J Coat. Technol. 60, (1988) No. 764, 43 and Proc. Water-Borne Higher Solids Coatings Symp. New Orleans, 1989, 332). All the stated publications concern paint binders which essentially harden by the reaction between hydroxy-functionalised polymers and amine resin or isocyanate cross-linkers; the low molecular weight hydroxyalkyl carbamates used are only used as reaction diluents and do not take part in the actual cross-linking reaction.
Another group of carbamate-containing binders are the polyfunctional hydroxyalkyl carbamates, which also fall within the known state of technology. In such binders, the hydroxyalkyl urethane function is linked to a polymeric system. This chiefly relates to:
a) Modified amine resins or mixtures with melamine resins (e.g. EP 152 820, EP 245 700, EP 245 701, EP 246 483, EP 257 848),
b) Acrylic resins with at least two hydroxyalkyl carbamate groups (e.g. EP 152 820, U.S. Pat. No. 4,758,632),
c) Polyfunctional hydroxyethyl carbamates based on amidoamines (e.g. U.S. Pat. No. 4 588 783),
d) Modified epoxyresins (e.g. EP 119 769, DE-OS 3 311 517, DE-OS 3 311 518, U.S. Pat. No. 4 484 994).
All of the hydroxyalkyl carbamates of this group are used as activated hydroxy-functionalised polymers. At high temperature they cross-link with normal amine resin cross-linkers, e.g. with melamine resins. With suitable catalysts these resins are also capable of self-crosslinking.
In hardening paint systems, similar functions are performed by hydroxyalkyl urethanes derived from low molecular weight di- or polyamines and ethylene or propylene carbonate (e.g. V V Mikheev et al., Lakokras. Mater. Ikyh Primenen. 1983, No. 6, 5; G G Parekh, Proc. Water-Borne Higher-Solids Coatings Symp. New Orleans, 1987, 492), which are also used for cross-linking with polyfunctional hydroxycompounds.
It is also known that carbamates can react with epoxy groups. Y Iwakura and S Izawa describe reactions of N-aryl urethanes with arylglycidyl ethers (J Org. Chem. 29, (1964) 379; J Polym. Sci. A-14, (1966) 751). With the use of bifunctional starting compounds, linear polymers can be prepared. After a number of attempts, it had to be stated that N-alkyl carbamates do not undergo this reaction.
Linear polymers from bifunctional epoxides and bifunctional carbamates were obtained by Z N Pazenko et al. (Sintez i fizikochimija polimerow 7, (1970) 42; 8, (1971) 45) In these cases also, N-aryl carbamates were used. The polymers obtained have low molecular weights, melt easily and dissolve well in most polar solvents.
The same authors also state (Sintez i fizikochimija polimerow 6, (1970) 42), that under severe reaction conditions (ca. 1-2 hours at ca. 160.degree. C.) unsubstituted aliphatic carbamates can also be made to react with epoxides. In the process readily melting and easily soluble--therefore linear--polymers with low molecular weight are likewise obtained.
Cross-linking systems from hydroxyethyl urethanes and epoxy resins were obtained by G Rokicki and R Lazinski (Angew. Makromol. Chem. 170 (1989) 211). Here epoxides were cross-linked with aliphatic polyamines (e.g. triethylenetetramine), which were partially modified with cyclic carbonates. The modified polyamines contain hydroxyethyl urethane groups, however also at the same time adequate amounts of reactive aliphatic H-N-functions, through which the actual cross-linking reaction proceeds--at room temperature. This case involves classical epoxide hardening by aliphatic polyamines: the hydroxyalkyl urethane groups serve only to improve the properties of the products obtained, without strictly speaking being involved in the cross-linking reaction.
Attempts to prepare three-dimensional networks from polyfunctional epoxides (epoxyacrylates) and bifunctional hydroxyalkyl carbamates are described by V V Mikheev et al. (Lakokras. Mater. Ikh Primenen. (1987), No. 5, 13; (1987), No. 6, 26). It seems that here one is dealing with a reaction between the epoxy groups and the hydroxyurethane functions, since the resulting products are cross-linked. However, the cross-linking reaction--which is catalysed by organotin compounds--requires high temperatures of ca. 160.degree. to 180.degree. C. and quite long reaction times (up to 2 hours or more). Under these very severe conditions, undesired decomposition processes of the polymeric system, e.g. a marked yellowing in the case of stoving enamels, are often observed.
The known state of technology therefore offers no convenient possibility for the production of cross-linked systems from epoxide resins and carbamates, in particular hydroxyalkyl urethanes or derivatives thereof.